Cyclospora cayetanensis was identified as a coccidian in 1993 by Dr. Ynes Ortega, a Peruvian investigator who named the organism for Cayetano Heredia, the University in Peru where initial work was performed. In areas of endemnicity in Peru, Guatemala, and Nepal, Cyclospora has been shown to be a fairly common enteric pathogen among children living in poor communities. Large outbreaks of cyclosporiasis in North America in 1996, 1997 and 1998 have been linked to ingestion of contaminated imported fresh produce. The overall aim of this study is to apply the newly developed tools of Cyclospora Immunoblot assay, PCR-based detection in stool specimens, water and sewage, and molecular genotyping to further our understanding of the epidemiology of Cyclospora cayetanensis. Specifically we will1, determine the seroprevalence of Cyclospora using an immunoblot assay in communities of different geographical locations ; 2, use of PCR in field studies as a sensitive and specific method to detect Cyclospora in stool specimens, water and sewage; and 3, determine the sensitivity of PCR performed on rectal swab specimens as a detection method compared to PCR and microscopic examination of whole stool specimens. T o better define the epidemiology of Cyclospora we will evaluate potential risk factors associated with Cyclospora infection over different ecologic zones, variations in socioeconomic status, and within an endemic community , and examine genotype variations in families with more than one infection, and in individuals infected more than once. Under this TMRC program approach, this component will primarily emphasize the use of new techniques (molecular epidemiology, immunological assays, GPS/GIS) towards the characterization of the epidemiology and transmission of Cyclospora.